1. Technical Field
The present invention relates generally to a steering apparatus for steering rear wheels of an automotive vehicle. More particularly, the invention relates to an improved steering apparatus which has a variable maximum steering angle for rear wheels dependent upon a vehicle speed.
2. Background Art
Various types of steering actuators for rear wheels have been proposed. Japanese Patent First Publication No. 63-207773 discloses a steering actuator which includes a single electric motor and a ball screw mechanism wherein the electric motor is driven according to a steered angle of front wheels to steer the rear wheels by a preselected angle.
The prior art steering actuator having a signal motor is operable to control a rotational angle and a rotational direction of the motor so as to provide a steering direction and a steering angle for rear wheels according to a vehicle speed and a steered angle of front wheels which are electronically monitored by sensors. This system requires highly precise control because the front and rear wheels are not mechanically communicated with each other to steer the rear wheels independently. Thus over-running of the motor due to malfunction of a control system sometimes causes unanticipated vehicle behavior. For example, steering the rear wheels at a maximum steering angle while the vehicle runs at high speed may induce the wheels to spin, resulting in unstable cornering.